LONDON (Reuters) - British Prime Minister Boris Johnson’s plan to break international law by breaching parts of the Brexit divorce treaty with the European Union faces a vote in parliament on Monday amid growing opposition from within his own party.

The House of Commons will debate the Internal Market Bill, which the EU has demanded Johnson scrap by the end of September. After the debate, lawmakers will vote to decide if it should go to the next stage. That vote may come late.

Johnson’s decision to explicitly break international law has plunged Brexit back into crisis less than four months before Britain is finally due to leave the EU’s orbit at the end of a post-Brexit transition period.

The EU has ramped up no-deal Brexit preparations while Britain has dismissed an ultimatum from Brussels to scrap the main parts of the bill by the end of September.

Johnson, who has a majority of 80 in the lower house of parliament, is facing a growing revolt from some of his own lawmakers. Former prime ministers John Major, Tony Blair, Gordon Brown and Theresa May have criticised the plan.

“When the queen’s minister gives his word, on her behalf, it should be axiomatic that he will keep it, even if the consequences are unpalatable,” Johnson’s former Attorney General Geoffrey Cox said in The Times.

“No British minister should solemnly undertake to observe treaty obligations with his fingers crossed behind his back,” said Cox, who was sacked by Johnson in February.

Former PM Cameron says he has misgivings about Brexit move Goldman Sachs says pound levels now attractive British ministers say the bill, which explicitly states that it could be inconsistent with a host of international laws, is intended to clarify ambiguities and act as a safeguard in case the trade talks fall.

“Having an insurance policy seems to me sensible,” junior interior minister Kit Malthouse said.

But some EU diplomats say they think London is playing a game of Brexit chicken, inviting the collapse of trade talks to either get the deal it wants or to leave without a deal.

The EU says it cannot trust those who break agreements and that if the bill is not effectively scrapped there will be no trade deal to cover everything from car parts to food.

“Come back from the brink, re-establish trust and keep your word,” Ireland’s European Affairs Thomas Byrne said.